Manufacture of motor fuels



PATENT OFFICE MANUFACTURE or Moron-roars Vladimir Ipatiefl and Raymond E. Schaad,

Chicago, Ill., assignors to Universal Oil Products Company, Chicago, 111., a corporation of Delaware v Drawing. Application April18, 1936, Serial No. 75,227

1 Claim.

This invention relates particularly to the manufacture of motor fuel of high antiknock value.

In a more specific sense it is concerned with a process involving a cooperative series of steps I whereby substantially saturated motor fuel fractions of high antiknock value are produced from normally gaseous olefin hydrocarbons.

Owing to the comparatively recent adoption of high compression ratios in intemal combustion engines of the spark ignition type, following the discovery that increased ratios gave much greater thermo-dynamic efficiencies, there has been a rapidly increasing demand for high antiknock value motor fuels and-much experimenting I has been conducted to determine the types of combustible fluids which could be used in high compression engines without knocking. The general results of these researches have indicated that within the customary volatility range of I automotive fuels, say from approximately 100 to 400 F., the antiknock value of the various hydrocarbon groups decreases generally in the order aromatics, oleflns, naphthenes, and parafflns. However, there are certain very definite I anomalies in the case of hydrocarbons of mixed character such as, for example, alkylated aromatics or naphthenes and in the case of chain compounds of isomeric or more compact molecular structure. For example, for a given molecular weight or a given number of carbon atoms, an isomeric parafiin may have better antiknock characteristics than a straight chain olefin. In the case of olefins, the position of the double bond also has a definite influence. These considera- Sl tions are briefly presented to furnish a background to show the character of the present invention as an improvement in the art of manufacturing high antiknock fuels. 1

The cracking process is generally resorted to 40 for producing gasolines of superior antiknock value, butwhen the attempt is made to exceed a certain octane number in the product by increasing the severity of cracking conditions, there are sharp reductions in yield and the cost of producdl inggasolines having octane numbers of over by the C. F. R. motor method of testing is generally prohibitive under present market conditions. At the same time there is an increasing demand for fuels with octane numbers above this value for 50 use in aviation engines, and the specifications for these fuels require a high stability and a minimum of gum-forming tendencies. The present process a is concerned with the production of close cut hydrocarbon fractions similar in character to isoll octane which are made available in quantity for blending with gasolines of inferior knock rating, and particularly for use in aviation fuelblends which must have a specially high antiknock value in combination with substantially complete saturation.

In one specific embodiment, the present invention comprises polymerizing isobutene by means of solid phosphoric acid catalysts at temperatures and pressures corresponding to substantially vapor phase conditions of operation, 19 separating the liquid polymers comprising principally iso-octenes and controllably hydrogenating said iso-octenes to produce a product having substantially 100 octane number and the stability required in aviation fuels. 1

In another embodiment, the invention comprises subjecting a mixture of propylene and butenes to polymerization in the presence of solid phosphoric acid catalyst first at between 200 and 250 F. to polymerize isobutene and then go at temperatures from 250 to 500 F. to polymerize propylene and n-butenes.

A particular feature of the present invention is the utilization of a constituent of cracked hydrocarbon gas mixtures to produce a product as approximating iso-octane in composition and properties. In the presence of the preferred catalyst to be presently described and under the preferred range of operating conditions in respect to temperature, pressure and time of contact, we 30 have found that it is possible and practical to more or less selectively polymerize iso-butene as it occurs in cracked gas mixtures or particular fractions thereof such as stabilizer refluxes to form a mixture of dimers which when hydroa5 genated approach the iso-octane commonly used as a standard of antiknock value in composition and properties. This reference compound is ordinarily produced by synthetic processes and is known to be principally the isomer designated as a 2,2,4-trimethylpentane. The product of the present process contains major percentages of this compound and when produced from close fractions and under closely regulated conditions may be over of the standard reference hydroa carbon, octane numbers being not infrequently as high as 98 to 100.

Depending upon the relative proportions of iso and normal butenes in gas mixtures subjected to treatment by the present process, a variable 50 amount of the n-butenes may polymerize with .the isobutene to form different types of isomeric octenes. These mixed polymers have been found to hydrogenate principally to the compound 2,2,3-trimethylpentane, a compound closely re ll lated in properties to the iso-octane described in the preceding paragraph. The antiknock value oi this hydrocarbon is also very high. While it is recognized as being impossible to entirely prevent the polymerization of n-butenes either among themselves or with isobutene, the present process closely approaches the conditions under which aminimum of such polymerization reactions occurs so that the main product of the polymerizing step is di-isobutene.

The catalytic material which has been found suitable for thus selectively polymerizing the butanes present in hydrocarbon mixtures has been designated above as solid phosphoric acid". This term is generally applicable to composite granular materials made by the general procedure of incorporating a liquid phosphoric acid such as ortho or'pyrophosphorlc acid with a relatively inert and generally siliceous adsorptive carrying and spacing material such as, for example, kieselguhr, and calcining at a fixed temperature to produce a solid cake which is ground and sized to produce catalytically active granules which are utilizable in treaters as filling material. In the present instance to accomplish the desired selective polymerization of iso-butene from mixtures, it is essential to employ a relatively "wea phosphoric acid-absorbent mixture such as that produced by incorporating 30 parts by weight of orthophosphoric acid with 70 parts by weight of a siliceous carrier such as kieselguhr. It has been determined that isobutene under the temperatures, pressures and times of contact which characterize the present process is readily polymerized by such solid composites while the n-butenes and the still less reactive propylene and ethylene are not affected. As a rule primary composites embodying less than by weight of liquid phosphoric acid will be more or less of a dry cake and require no extensive calcining. In case of the 30-70 mixes which are conveniently employed according to the present process these are preferably pelleted to produce small catalyst particles. Using a catalyst of the above character as filler in a tube or chamber, hydrocarbon fractions such as, for example, stabilizer refluxes or the so-called B- fractions produced therefrom by further fractionation are passed through the catalyst mass at temperatures within the approximate range of ZOO-230 Rand pressures oi the order of 100 pounds per square inch, which conditions in the case of fractions comprising principally hydrocarbons of 3 and 4 carbon atoms are suilicient to maintain practically vapor phase conditions with very little condensation of the original gaseous hydrocarbons though some condensation of liquid polymers may occur. It will be obvious to those properly skilled in processes of the present character that there will need to be some latitude in the conditions employed on mixtures which vary markedly in the percentage of isobutene and the proportions of isobutene and n-butenes, but the conditions thus far enumerated are applicable to the great majority of gas mixtures encountered as by-products in cracking plants.

Following the catalyst chamber in the operation of the process on ordinary stabilizer refiuxes the total products are cooled and condensed and the liquid polymers which will consist principally of 2,4,4-trimethylpentenes are stabilized under any set of conditions necessary for removing residual unaffected olefins and other gases and the gases may if desired be further fractionated or subjected directly to more intensive conditions of aaoanoc treatment to eiiect the polymerization oi residual n-butene and propylene. The amount of polymer actually due to the polymerization of isobutene and that produced by the concurrent polymerisation of isobutene with alpha and beta butenes 5 will obviously depend upon the ratio 01' these compounds in the original mixture treated. Under some conditions there may be some simple polymerization among the n-butenes,-particularly when these compounds are present in large excess over the amount of isobutene. The propylene is substantially unaffected under the pre- Ierred conditions of operation. A subsequent example will indicate the degree of selectivity to be expected in subjecting mixtures containing both isobutene and the normal butenes to the action of the preferred catalyst.

As a final step in the present process the polymer consisting principally of 2,4,4-trimethylpentenes is hydrogenated to produce principally isooctanes. The details of this step are simple and consist merely in passing the vapors of the stabilized polymer product mixed with a moderate excess of hydrogen over that required for complete saturation over catalysts which are known to be effective in promoting and accelerating hydrogenation reactions. Such catalysts are, for example, the metals and the oxides of the iron group, particularly nickel, and in case there is danger of sulfur contamination, the oxide or sulfides of chromium, molybdenum and tungsten may be used which are generally designated as "sulfactive catalysts. The temperatures necessary for the hydrogenation reactions are of the order of 600 to 800 F. under pressures of approximately 200 to 400 pounds per square inch. Following the hydrogenation step the saturated product is separated'i'rom residual fixed gases, principally hydrogen, and may be passed to storage with or without a light chemical treatment such as, for example, washing with caustic soda to remove traces of sulfur compounds.

The hydrogenation of the olefin polymer may be conducted using a reduced nickel catalyst prepared by passing hydrogen over the oxide for a long time at 572 F. With this catalyst substantially complete hydrogenation may be efl'ected at a temperature of 428 F. and a pressure of the order of 2000 pounds per square inch. Using a nickel thiomolybdate catalyst, a temperature of from 600-800 F. and a pressure about 215 pounds per square inch are satisfactory, this corresponding to a vapor phase operation.

The following examples are given to indicate the character of the results which are obtainable by the use of the process though without the intent of unduly limiting the scope of the invention in exact accordance with the data presented.

Example I The fraction treated was a out which consisted principally of the four-carbon atom aliphatic hydrocarbons produced by close fractionation of the gases produced from an oil cracking plant. It had the following composition by weight:

Per cent 16.8

Isobutene n-Butene 36.0 n-Butane 47.2

of about 4 mm. The average temperature throughout the catalyst mass was 210 F. The pressure was 100 pounds per square inch and the vaporous hydrocarbon mixture was passed through the catalyst bed at the rate of 4 cubic feet of gas under standard conditions per hour per pound of catalyst. An analysis of the liquid product indicated that in this single once through operation 90% of the isobutene and of the n-butenes were polymerized, which indicates a marked degree of selectivity under these conditions. The liquid polymer corresponded to 4.8 gallons per 1000 cubic feet of gas mixture, and 3.8 gallons or 80% of the stabilized liquid polymers were found to be 2,2,4-trimethylpentene.

The stabilized polymer product was then vaporized and passed at a temperature of about 575 F. over a catalyst composite comprising molybdenum trioxide as its active constituent, in admixture with an amount of hydrogen corresponding to'a excess over that required for complete saturation of the olefins. on cooling and condensation of the hydrogenated product it was found to be a liquid boiling within the range of 210-250 F. and having an octane number of 98 by the C. F. R. motor method of testing.

' Example II Isobutene of approximately 95% purity was contacted with a weak phosphoric acid catalyst comprising 30% of 89% orthophosphoric acid and of diatomaceous earth at a temperature of 210-220 F. under 100 lbs. pressure. During a run of 65 hours duration there was a production of 21 gallons of polymers per lb. of catalyst. This was then distilled to throw over 97% of the total and the distillate was then hydrogenated at 428 F. in the presence of 10% by weight of nickel oxide catalyst. The maximum pressure employed in the hydrogenation was 150 atmospheres.

Properties of the isobutene polymer and of the hydrogenated polymer are given in the following table:

Total product, B. P., F... 194-427 192-400 Blending Octane number.-- 128 92 Octane No Octane No. with 2 cc. tetra ethyl lead/gal 87 100 C; out used, B. P., F 212-230 205-216 Percent of total product 56 59 Blending octane number. 136 96 Octane No 85 100 Octane No. with 2 cc. tetra ethyl lead/gal 100 O cut used, B. P., F 338-347 338-356 Percent of total product 38 28 Blending octane number. 96 Octane N o 85 "100 97% by volume of tho olefin.

Approximately.

The character of the present invention can be seen from the preceding specification and its commercial importance is evident from the data presented in the examples, although neither section is to be considered as unduly limiting its generally broad scope.

We claim as our invention:

A process for producing di-isobutene from a normally gaseous mixture consisting essentially of four carbon atom hydrocarbons and containing isobutene and normal butenes, which comprises subjecting said mixture in vapor phase at a temperature of about 210 F. and under a pressure of about 100 pounds per square inch to the action of a siliceous catalyst containing approximately 30% phosphoric acid, whereby to selectively polymerize the isobutene.

VLADIMIR IPATIEFF. RAYMOND E. SCI-IAAD. 

